Ferrule-type tube fittings are well known in the art. A two ferrule fitting that has been highly successful for over 30 years is a sequential gripping arrangement invented by Lennon, et al., U.S. Pat. No. 3,103,373, the entire disclosure of which is fully incorporated herein by reference.
In a typical ferrule-type tube fitting assembly there is a coupling arrangement that includes a coupling body and a coupling nut that is threadably engaged with threads on one end of the coupling body. The coupling body includes a torquing flange, typically in the form of a hex shaped flange. The coupling body at the other end may be joined to or integral with another body, flow control device and so on. The coupling body includes an axially tapered opening or camming mouth and a shoulder or stop axially spaced from the tapered opening. Two gripping components or ferrules, including a rear ferrule and a front ferrule, are positioned within the coupling nut and are interposed between the coupling body and the coupling nut. The tapered front end of the front ferrule initially engages the camming mouth of the coupling body and a tapered front end of the rear ferrule initially engages a camming surface at the back end of the front ferrule. The coupling nut has a shoulder that drivingly engages a back wall of the rear ferrule. A tube end is axially inserted into the fitting until the tube end abuts the inner shoulder stop of the coupling body. Upon relative rotation of the coupling body and nut which drives the coupling components axially towards each other, the tapered ferrules are axially pulled together, commonly referred to in the art as being “pulled-up”, and radially displaced inwardly to cause a sequential inward gripping of the tube. The ferrules tightly grip the tube wall due to the swaging action.
Typically, a tube fitting assembly such as described above, is shipped to a customer in an assembled condition with the ferrules installed in the coupling nut and the coupling nut threaded onto the coupling body to a finger tight condition. The assembler then slips a tube end axially into the fitting until it bottoms or abuts the inner stop shoulder on the coupling body. With the fitting in an initial finger tight condition, the assembler, using a wrench or spanner or the like for example, then imparts a relative rotation between the coupling body and the coupling nut for a predetermined rotation to complete the installation. For smaller tube fittings, for example tube fittings used on one-quarter (¼) to one (1) inch tubing, there is typically a relative rotation of one and a quarter “turns past finger tight” (“TPFT”) position to achieve proper initial pull-up.
The number of turns to properly pull-up a fitting assembly is determined by a number of factors including the thread pitch and the proper axial displacement of the coupling nut relative to the coupling body to insure that the ferrules are properly swaged onto the tube wall. Although the various parts of the fitting are machined with high precision and assembled to a finger tight position, it still can be difficult to keep track of the number of rotations and fractions thereof to pull-up the fitting. Many times the fitting is being installed in an area with limited clearance for the wrench, thus necessitating a number of separate wrenching operations for one complete rotation.
A successful and commonly used solution to verifying proper pull-up is a NO-GO gauge as described in U.S. Pat. No. 3,287,813 to Lennon et al., the entire disclosure of which is fully incorporated herein by reference. This gauge effectively verifies that the gap or relative spacing between the coupling body flange and the forward end of the coupling nut is of the correct dimension. The assembler first imparts the required relative rotation between the coupling nut and body. If the gauge cannot fit between the body and the coupling nut, the assembler knows that the nut has at least been properly pulled-up.
Although the gauging tool described above continues to enjoy excellent commercial success and use, there are applications where the use of the gauge may be an inconvenience. Of particular interest is the need for a gauge that does not necessarily require a separate gauge tool, but rather could be intrinsically part of the fitting.
Additionally, the NO-GO gauge is used principally for initial pull-up of the fitting assembly. In some cases, a coupling may be disassembled by unthreading the coupling nut from the body for repair or replacement of the device joined to the tube end. During remake of the fitting, typically the relative rotation between the coupling nut and body requires fractionally more turns than is required for initial pull-up, or in other words the axial displacement of the coupling nut towards the coupling body is slightly greater each pull-up compared to the previous pull-up operation. A manufacturer may determine a recommended number of remakes or axial displacement of the coupling nut with respect to the coupling body based on a predetermined amount or axial displacement beyond the initial pull-up position. The design factors taken into consideration may include the pressure and temperature ratings for the fitting, the materials used in the tubing and the fitting components and so on.
The actual number of remakes a given fitting assembly can undergo and still exhibit acceptable performance characteristics may be significantly higher than a recommended distance of additional axial displacement past the initial pull-up position, but it may still be desirable in some cases to be able to provide an indication to the assembler that the fitting assembly has been remade a number of times so as to have advanced the coupling nut and body together a predetermined axial displacement beyond initial pull-up. Since the hand gauge discussed above necessarily has a fixed axial dimension, it is not useful for verifying additional axial displacement for remade fittings.
It is therefore an objective of the present invention to provide apparatus and method for verifying proper pull-up of a ferrule-type tube fitting for initial pull-up. It is another objective to provide apparatus and method that verifies proper initial pull-up and also can be used to provide an indication that the fitting has been remade a number of times so as to indicate a predetermined axial displacement of the coupling nut relative to the coupling body.